1. Field of the Invention
The present invention relates to an image projection apparatus that projects an image, a control method of the image projection apparatus, and a computer-readable storage medium.
2. Description of the Related Art
Conventionally, in a high pressure mercury lamp widely used as a light source of a projector, an arc discharge between a pair of electrodes provided in an arc tube is utilized to cause mercury vapor (light emitting material) included in an inside of the arc tube to emit light. While mercury vapor returns to liquid when a power source of the projector is turned off, there is a case where liquid mercury adheres to the pair of electrodes on this return occasion and thereby a short circuit (shunt) is caused between the electrodes. This symptom is called “mercury bridge” and leads to a failure in lighting the lamp of the projector.
The mercury bridge is caused depending on two characteristics that liquid mercury tends to adhere to a portion at a low temperature, and that the electrode portion tends to change in temperature compared to a tube portion (light emitting tube) and the temperature at the electrode portion tends to become lower than that at the tube portion after the power source of the projector is turned off. Especially due to a correlation between the electrode temperature and a lamp power (power to be supplied to the electrodes), a difference in temperature between the electrode portion and the tube portion becomes large when the power source of the projector is turned off from a state where the lamp power is low, thereby dramatically increasing the probability of the occurrence of the mercury bridge.
Then, already known has been a technique of performing an after-cooling operation in which the lamp is kept cooled for a certain period of time after the power source of the projector is turned off to make the difference in temperature between the electrodes and the tube portion small and the probability of the occurrence of the mercury bridge low. For example, Japanese Patent No. 4070420 discloses a technique of turning off the power source after keeping the lamp power low for a certain period of time in turning off the power source of the projector to prevent the mercury bridge.
However, since the mercury bridge is prevented by reducing the lamp power, then lowering the temperature at the tube portion to be equal to or less than the boiling point of the mercury, and liquefying the mercury in the tube portion after the operation of turning off the power source in Japanese Patent No. 4070420, there is a problem of taking a long time until the lamp is turned off after the power source is turned off.
Therefore, there is a need for an image projection apparatus capable of shortening a time required until the lamp is turned off and preventing mercury bridge; and a control method and a computer-readable storage medium of the same.